JP2000228560A - Semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser and a method for manufacturing it containing a window structure that is manufactured simply at low cost. SOLUTION: A resonator's end surface 12c is formed by etching, and a side wall epitaxial growth layer 13 that is a semiconductor layer having a band gap wider than that of an active layer 12b of a resonator 12 is formed on the resonator's end surface 12c by side-wall epitaxial growing, and then a substrate 11 is divided at a position outer than the resonator's end surface 12c by cleaving or dicing, etc., so that the resonator's end surface 12c is positioned inner than a chip's end surface 11a of the substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-power semiconductor used for optical disks, solid-state laser excitation, laser beam printers, optical fiber amplifier excitation, optical communication, laser processing, laser treatment, and the like. The present invention relates to a method for manufacturing a laser and a semiconductor laser.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for higher power semiconductor lasers as light sources for optical disks and laser printers, or as optical fiber amplifiers and light sources for exciting solid lasers. Often a problem with high power operation of semiconductor lasers is catastrophic failure due to deterioration of the light emitting end face induced by high light density. This problem occurs particularly remarkably in a short-wavelength semiconductor laser containing Al. For this reason, a structure (hereinafter, referred to as a “window region”) having a band gap wider than that of the active layer, that is, a region including a semiconductor layer exhibiting non-absorptivity to oscillation light (hereinafter, referred to as a “window region”) is provided around the light emitting end face (hereinafter, referred to as a structure). The above problem is solved by adopting a “window structure”).

In a semiconductor laser having such a window structure, for example, in a manufacturing process of a pn-embedded laser, an active layer in a window region is etched and removed at the same time as stripe formation etching, and the removed portion is entirely pn-embedded. It can be manufactured by growing (hereinafter referred to as “pn buried growth method”) (for example, see “Electron. Lett.” Vol. 30; p. 1766; (1994) and the like).

Further, for example, in a manufacturing process of a quantum well semiconductor laser, by diffusing impurities into a window region or performing a heat treatment after ion implantation, the quantum well in the window region is mixed and made non-absorbing ( (Hereinafter, referred to as “quantum well alloying method”) (for example, “The 58th Annual Meeting of the Japan Society of Applied Physics”, p. 1127; 4a-ZC-12; (March 1997 ), `` Proceedings of the 45th Joint Lecture on Applied Physics, '' p. 1113; 29a-ZH-9;
(March 1998) etc.).

Further, for example, in a general semiconductor laser manufacturing process, a wafer is divided into strips by cleaving or dicing to form chip end faces constituting a resonator, and a large number of laser elements are arrayed. It can also be manufactured by epitaxially growing the semiconductor layers on the chip end faces in a state where they are arranged (hereinafter referred to as "bars") (hereinafter referred to as "epitaxial growth method on chip end faces") (for example, Japanese Patent Application Laid-Open No. H5-251824). Reference).

[0006]

In a semiconductor laser having a window structure as described above, it is preferable that the window region be non-conductive because good device characteristics can be obtained. Because if the window area is conductive,
This is because an increase in the threshold value and a decrease in the differential efficiency due to the reactive current to the window region and the increase in the internal loss of the resonator due to free carrier absorption are inevitable. Further, in order to suppress an increase in threshold value and a decrease in differential efficiency due to divergence of oscillation light in the window region, the window region desirably has an optical waveguide structure.

However, the semiconductor laser manufactured by the pn buried growth method described above has no optical waveguide structure in the in-plane direction of the epitaxial layer in the window region (hereinafter referred to as "lateral direction"), and furthermore, the window region has a p-type structure. Since it must be n-type, by controlling the length of the window region, it is necessary to suppress the divergence of oscillation light in the window region, the increase in threshold value due to free carrier absorption, and the decrease in differential efficiency. In the pn buried growth method described above, it is very difficult to increase the division accuracy such as cleavage for determining the length of the window region (normally about ± 10 to 20 μm at production level, and preferably about ± 5 μm at the production level). Could not do. Also,
Since it is based on a pn-embedded laser, it cannot be applied to the manufacture of a ridge waveguide type laser having excellent productivity.

In the above-described quantum well alloying method, since a window structure is manufactured by thermal diffusion or ion implantation, it is difficult to make the window region non-conductive. In many cases, the window region becomes conductive. As a result, reactive current is injected into the window region, and the threshold value increases. As one method for solving this problem, semi-insulation is performed by injecting protons into the window region. However, in the semiconductor laser having the window structure manufactured in this manner, although the initial characteristic value is significantly improved, the injected protons move during long-term operation, and thus high reliability is maintained for a long time. It was difficult. Further, since it is assumed that the semiconductor laser has a quantum well active layer, it cannot be applied to a semiconductor laser having a bulk active layer.

On the other hand, in the above-described epitaxial growth method on the chip end face, since a window structure having a thickness of several tens to several hundreds of nm is manufactured by epitaxial growth on the chip end face, problems such as divergence of oscillation light and injection of reactive current actually occur. However, since the width of the bar was very small, being several hundreds of μm, the handleability was very poor. Further, since it is assumed that epitaxial growth is performed on the side surface of the bar, the manufacturing efficiency is very poor.

Accordingly, an object of the present invention is to provide a semiconductor laser having a window structure which can be easily manufactured at low cost and a method of manufacturing the semiconductor laser.

[0011]

According to a first aspect of the present invention, there is provided a semiconductor laser in which a resonator end face is located inside a chip end face of a substrate and an active layer of the resonator is located between the chip end face and the active layer. A semiconductor layer having a wide band gap is provided on the end face of the resonator.

According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor laser, comprising: forming a cavity facet by etching; and forming a semiconductor layer having a band gap wider than an active layer of the cavity. After the side walls are epitaxially grown on the end face of the resonator, the substrate is divided at a position outside the end face of the resonator.

A semiconductor laser according to a third aspect of the present invention for solving the above-mentioned problem is characterized in that it is manufactured by the method for manufacturing a semiconductor laser according to the second aspect of the present invention.

[Operation] According to the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention, the semiconductor layer having a band gap wider than the active layer of the resonator is formed by epitaxially growing the side wall on the end face of the resonator. The window region can be made much shorter than the length determined by the accuracy of division such as dicing or the like, and the threshold value due to injection of reactive current into the window region and diffusion of oscillation light in the window region and absorption of free carriers. In addition to avoiding an increase and a decrease in differential efficiency, the present invention can be widely applied regardless of the structure of the active layer or the waveguide structure in the active layer region. Further, after forming the resonator end face by etching, and after forming the semiconductor layer on the resonator end face, the substrate is divided, that is, the resonator end face is formed by etching without division such as cleavage or dicing, Since the semiconductor layer is formed before cutting into the bar state, the semiconductor layer can be efficiently manufactured.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of a semiconductor laser and a method of manufacturing a semiconductor laser according to the present invention will be described below, but the present invention is not limited to these embodiments.

[First Embodiment] A first embodiment of a semiconductor laser and a method of manufacturing a semiconductor laser according to the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing a schematic structure of the semiconductor laser.
This is the case where an aAs-based single or multiple strained quantum well active layer is applied.

First, a wafer is prepared by epitaxially growing a resonator 12 comprising a GaAlAs cladding layer 12a and an InGaAs-based strained quantum well active layer 12b on a GaAs substrate 11. Here, the InGaAs used for the strained quantum well active layer 12b is usually made of Ga
Although not lattice-matched with As, if the film thickness is extremely small, the crystal can grow without causing lattice defects due to distortion of the crystal.

Next, a ridge waveguide is formed on the wafer by etching. After depositing an insulating film on the wafer, electron cyclotron resonance (ECR) using a mixed gas of boron trichloride (BCl ₃ ) gas and argon (Ar) gas
The resonator end face 12c is formed in a stripe shape (width 40 μm, depth 15 μm) in a direction perpendicular to the ridge waveguide by plasma etching.

After the etching, a treatment with a sulfuric acid (H ₂ SO ₄ ) -based etchant is performed, and metal organic chemical vapor deposition (MOV) is performed.
PE) method, a sidewall epitaxial growth layer 13 of GaAs which is a semiconductor layer having a band gap wider than that of the strained quantum well active layer 12b and exhibiting non-absorptivity to oscillation light.
(Thickness: 100 nm) is formed by epitaxially growing sidewalls on the cavity facet 12c.

After the window structure is manufactured in this manner, after forming the surface electrodes, the cavity end face 1 on the front side is formed.
An antireflection film is formed on the side wall epitaxial growth layer 13 of 2c, and a reflection film having high reflectivity is formed on the side wall epitaxial growth layer 13 on the cavity end face 12c on the rear side. Subsequently, after polishing the substrate 11, a back electrode is formed.

Next, the substrate 11 is divided by cleavage, dicing, or the like at a position outside the resonator end surface 12c, and the substrate 11 is divided into the chip end surface 11a of the substrate 11 inside.
The wafer is formed in a strip shape so that 2c is located, and is prepared in the bar state (width of 700 to 1000 μm, length of 10 mm), divided into chips, and then packaged.

The semiconductor laser thus manufactured oscillates at a wavelength of 980 nm, has a threshold current of 28 mA,
The maximum light output was 700 mW.

Such a semiconductor laser has an emission wavelength of 9
Since it is 80 nm, it is suitable for a light source for exciting an Er-doped optical fiber. Further, by changing the mixed crystal ratio and the film thickness of the strained quantum well active layer 12b, the wavelength of 900 to 110
A semiconductor laser of 0 nm can be manufactured.

[Second Embodiment] A second embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view showing a schematic structure of the semiconductor laser.
This is the case where a bulk active layer of 1As is applied.

First, a wafer is prepared by epitaxially growing a resonator 22 comprising a GaAlAs cladding layer 12a and a GaAlAs bulk active layer 22b on a GaAs substrate 11. Next, a ridge waveguide is formed on the wafer by etching. After depositing an insulating film on the wafer, E using mixed gas of BCl ₃ gas and Ar gas
The resonator end face 22c is formed in a stripe shape (width 40 μm, depth 15 μm) in a direction perpendicular to the ridge waveguide by CR plasma etching.

After the etching, a treatment with an H ₂ SO ₄ -based etchant is performed, and a semiconductor layer having a wider band gap than the bulk active layer 22b and having a high Al composition and exhibiting non-absorptivity to oscillation light is formed by MOVPE. GaAs
lAs side wall epitaxial growth layer 23 (thickness 100 n
m) is epitaxially grown on the side wall of the resonator end face 22c.

After the window structure is manufactured in this manner, after the surface electrode is formed, the cavity end face 2 on the front side is formed.
An anti-reflection film is formed on the side wall epitaxial growth layer 23 of 2c, and a reflection film having high reflectance is formed on the side wall epitaxial growth layer 23 of the cavity end face 22c on the rear side. Subsequently, after polishing the substrate 11, a back electrode is formed.

Next, the substrate 11 is divided at a position outside the resonator end face 22c by cleavage, dicing, or the like, so that the substrate end face 2a is located inside the chip end face 11a of the substrate 11.
The wafer is formed in a strip shape so that 2c is located, and is prepared in the bar state (width of 700 to 1000 μm, length of 10 mm), divided into chips, and then packaged.

In the present embodiment, GaAlAs is used for the side wall epitaxial growth layer 23, but InGaP may be used instead.

[Third Embodiment] A third embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIG. FIG. 3 is a sectional view showing a schematic structure of the semiconductor laser.
This is a case where an aAs / GaAs quantum well active layer is applied.

First, a wafer is prepared by epitaxially growing a resonator 32 comprising a GaAlAs cladding layer 12a and a GaAlAs / GaAs quantum well active layer 32b on a GaAs substrate 11. Next, a ridge waveguide is formed on the wafer by etching. After depositing an insulating film on the wafer, a stripe shape (width of 40 μm, depth of 15 μm) is perpendicular to the ridge waveguide by ECR plasma etching using a mixed gas of BCl ₃ gas and Ar gas.
μm) to form a resonator end face 32c.

After the etching, a treatment with an H ₂ SO ₄ -based etchant is performed, and a GaAlAs semiconductor layer having a band gap wider than that of the quantum well active layer 32b and exhibiting non-absorptivity for oscillation light is obtained by MOVPE. Side wall epitaxial growth layer 23 (100 nm thick) is grown on the cavity facet 32c by side wall epitaxial growth.

After the window structure is manufactured in this manner, after the surface electrodes are formed, the resonator end face 3 on the front side is formed.
An anti-reflection film is formed on the side wall epitaxial growth layer 23 of 2c, and a reflection film with high reflectance is formed on the side wall epitaxial growth layer 23 on the cavity end face 32c on the rear side. Subsequently, after polishing the substrate 11, a back electrode is formed.

Next, the substrate 11 is divided by cleavage or dicing at a position outside the resonator end face 32c, and the resonator end face 3 is formed inside the chip end face 11a of the substrate 11 inside.
The wafer is formed in a strip shape so that 2c is located, and is prepared in the bar state (width of 700 to 1000 μm, length of 10 mm), divided into chips, and then packaged.

Although GaAlAs is used for the side wall epitaxial growth layer 23 in the present embodiment, InGaP may be used instead.

[Fourth Embodiment] A fourth embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view showing a schematic structure of the semiconductor laser.
This is a case where a bulk active layer of aP is applied.

First, the cladding layer 42a of InGaAlP
A wafer is produced by epitaxially growing a resonator 42 composed of a bulk active layer 42b of InGaP and an InGaP on a substrate 11 of GaAs. Next, a ridge waveguide is formed on the wafer by etching. After depositing an insulating film on the wafer, E using mixed gas of BCl ₃ gas and Ar gas
The resonator end face 42c is formed in a stripe shape (width 40 μm, depth 15 μm) in a direction perpendicular to the ridge waveguide by CR plasma etching.

After the etching, a treatment with an H ₂ SO ₄ -based etchant is performed, and the MOVPE method is used to form a semiconductor layer of InGaAlP, which is a semiconductor layer having a wider band gap than the bulk active layer 42b and exhibiting non-absorptivity to oscillation light. A sidewall epitaxial growth layer 43 (thickness: 100 nm) is epitaxially grown on the side wall of the resonator end face c.

After the window structure is manufactured in this manner, after the surface electrodes are formed, the resonator end face 4 on the front side is formed.
An anti-reflection film is formed on the side wall epitaxial growth layer 43 of 2c, and a reflection film having a high reflectance is formed on the side wall epitaxial growth layer 43 of the cavity end face 42c on the rear side. Subsequently, after polishing the substrate 11, a back electrode is formed.

Next, the substrate 11 is divided by cleavage, dicing, or the like at a position outside the resonator end face 42c, and the substrate end face 4a is formed inside the chip end face 11a of the substrate 11 inside.
The wafer is formed in a strip shape so that 2c is located, and is prepared in the bar state (width of 700 to 1000 μm, length of 10 mm), divided into chips, and then packaged.

[0041]

According to the semiconductor laser and the method of manufacturing the semiconductor laser of the present invention, a window structure of an extremely thin semiconductor layer is formed by epitaxial growth on the end face of the resonator. In this case, it is possible to avoid an increase in threshold value and a decrease in differential efficiency due to diffusion of oscillation light and absorption of free carriers.
Further, since the resonator end face is formed by etching, the semiconductor layer can be formed by side wall epitaxial growth before cutting into a bar state.

As a result, it is not necessary to perform epitaxial growth on the end face of the bar having poor handling properties, and a semiconductor laser having a window structure can be manufactured efficiently. Further, since the window structure is manufactured by the side wall epitaxial growth, a wide range of applications is possible regardless of the structure of the active layer and the waveguide structure in the active layer region.

Accordingly, the present invention provides a general-purpose semiconductor laser having a window structure having very excellent characteristics,
In addition, it is possible to promote higher performance and lower price of various devices using the same.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of a first embodiment of a semiconductor laser according to the present invention.

FIG. 2 is a sectional view showing a schematic structure of a second embodiment of the semiconductor laser according to the present invention.

FIG. 3 is a sectional view showing a schematic structure of a third embodiment of the semiconductor laser according to the present invention.

FIG. 4 is a sectional view showing a schematic structure of a fourth embodiment of the semiconductor laser according to the present invention;

[Explanation of symbols]

 Reference Signs List 11 substrate 11a chip end face 12, 22, 32, 42 resonator 12a, 42a cladding layer 12b strained quantum well active layer 22b, 42b bulk active layer 32b quantum well active layer 12c, 22c, 32c, 42c resonator end face 13, 23, 43 Sidewall epitaxial growth layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomohiro Shibata 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Jiro Tenmei 3- 192-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo No. Nippon Telegraph and Telephone Corporation F-term (reference) 5F073 AA74 AA83 AA88 BA02 BA06 BA07 BA09 CA04 CA05 CA07 CA14 DA26 DA31

Claims (3)

[Claims] 1. A resonator end face is located inside a chip end face of a substrate, and a semiconductor layer having a band gap wider than an active layer of the resonator is provided on the resonator end face. Semiconductor laser. 2. A resonator end face is formed by etching.
After producing a semiconductor layer having a band gap wider than the active layer of the resonator by side wall epitaxial growth on the resonator end face, the substrate is divided at a position outside the resonator end face. Production method. 3. A semiconductor laser manufactured by the method for manufacturing a semiconductor laser according to claim 2.